Low NOx burner for a water heater

ABSTRACT

A method of assembling multiple low NO x  burners including the step of assembling multiple bodies, each body including a multiple first burner ports connected to a first burner inlet and multiple second burner ports connected to a second burner inlet. The method also including the step of selecting one of the bodies and inserting a first inlet tube into the second burner inlet to provide a fuel/air mixture to the second burner ports at a first rate. The method also including the step of selecting one of the bodies and inserting a second inlet tube into the second burner inlet to provide the fuel/air mixture to the second burner ports at a second rate different than the first rate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 13/988,970 filed on May 22, 2013, which claims priority to PCTApplication No. PCT/CN2010/079314 filed on Dec. 1, 2010. The entirecontents of each of the foregoing applications are incorporated hereinby reference.

BACKGROUND

The present invention relates to water heaters, and more particularly toa low NO_(x) burner for a water heater.

Nitrogen oxides (NO_(x)) are formed during combustion. NO_(x) istypically generated by high temperature flames. A low NO_(x) burnerreduces the amount of NO_(x) formed during combustion. A lean-rich dualburner assembly combusts a fuel-lean fuel/air mixture with a lean burnerand combusts a fuel-rich fuel/air mixture with a rich burner. Alean-rich dual burner assembly reduces NO_(x) by decreasing flametemperature.

SUMMARY

The present invention provides, in one aspect, a method of assemblingmultiple low NO_(x) burners. The method including the step of assemblingmultiple bodies, each body including a multiple first burner portsconnected to a first burner inlet and multiple second burner portsconnected to a second burner inlet. The method also including the stepof selecting one of the bodies and inserting a first inlet tube into thesecond burner inlet to provide a fuel/air mixture to the second burnerports at a first rate. The method also including the step of selectingone of the bodies and inserting a second inlet tube into the secondburner inlet to provide the fuel/air mixture to the second burner portsat a second rate different than the first rate.

The present invention provides, in another aspect, a low NO_(x) burnerincluding a body including multiple first burner ports connected to afirst burner inlet and multiple second burner ports connected to asecond burner inlet and a removable inlet tube positioned in the secondburner inlet to provide a fuel/air mixture to the second burner ports.

The present invention provides, in another aspect, a tankless gas-firedwater heater including a burner, a heat exchanger, and a water conduit.The burner includes a body with an inner burner having a first burnerinlet and an outer burner having a second burner inlet and a removableinlet tube positioned in one of the first burner inlet and the secondburner inlet. The removable inlet tube has an arrangement of openings toprovide a desired fuel/air mixture to the respective inner burner andouter burner. The burner has an input of greater than 199,000 BTU perhour and is operable to generate products of combustion having desiredcharacteristics resulting at least in part from the removable inlet tubeutilized. The heat exchanger receives the products of combustion fromthe burner. The water conduit is positioned in the heat exchanger in aheat exchange relationship with the products of combustion.

Other features and aspects of the invention will become apparent byconsideration of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a low NO_(x) burner.

FIG. 2 is a partially exploded view of the low NO_(x) burner of FIG. 1.

FIG. 3 is a partially exploded view of the low NO_(x) burner of FIG. 1.

FIG. 4 is a perspective view of an inlet tube for use with the lowNO_(x) burner of FIG. 1.

FIG. 5 is a section view of the inlet tube of FIG. 4 along line 5-5.

FIG. 6 is a section view of the inlet tube of FIG. 4 along line 6-6.

FIG. 7 is a section view of the inlet tube of FIG. 4 along line 7-7.

FIG. 8 is a perspective view of a second embodiment of an inlet tube foruse with the low NO_(x) burner of FIG. 1.

FIG. 9 is a section view of the inlet tube of FIG. 8 along line 9-9.

FIG. 10 is a section view of the inlet tube of FIG. 8 along line 10-10.

FIG. 11 is a section view of the inlet tube of FIG. 8 along line 11-11.

FIG. 12 is a perspective view of a third embodiment of an inlet tube foruse with the low NO_(x) burner of FIG. 1.

FIG. 13 is a section view of the inlet tube of FIG. 12 along line 13-13.

FIG. 14 is a section view of the inlet tube of FIG. 12 along line 14-14.

FIG. 15 is a section view of the inlet tube of FIG. 12 along line 15-15.

FIG. 16 is a section view of the inlet tube of FIG. 12 along line 16-16.

FIG. 17 is a perspective view of a fourth embodiment of an inlet tubefor use with the low NO_(x) burner of FIG. 1.

FIG. 18 is a schematic view of a tankless gas-fired water heaterincluding multiple low NO_(x) burners of FIG. 1.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

A low NO_(x) burner 100 for a water heater is shown in FIG. 1. The lowNO_(x) burner 100 includes an inner burner 105, an outer burner 110, aburner port plate 115, and an inlet tube 120. As shown in FIG. 3, theinner burner 105 is formed from a single plate, with the edges of theplate mechanically secured to one another to create an opening at theupper portion of the inner burner 105. The burner port plate 115 ispositioned within this opening. The inner burner 105 includes an inlet125 fluidly connected by a flow path 130 to a series of inner burnerports 135 formed in the burner port plate 115. The inner burner 105 alsoincludes a channel 137 that is aligned with an inlet 140 of the outerburner 110. The channel 137 includes a stop 141 at the distal end of thechannel 137. The outer burner 110 is formed by two plates 143 and 144mechanically secured together to surround the periphery of an upperportion of the inner burner 105 and create a series of outer burnerports 150 between the upper portion of the inner burner 105 and theouter burner 110. The inlet 140 of the outer burner 110 is fluidlyconnected by a flow path 145 to the outer burner ports 150. As shown inFIG. 2, the inlet 140 includes a longitudinal axis 153 and a pair oflocating slots 154. The slots 154 define a vertical plane that includesthe longitudinal axis 153. As best shown in FIG. 3, the outer burnerports 150 are formed between each of the plates 143 and 144 and theinner burner 105 so that the inner burner ports 135 are sandwichedbetween the outer burner ports 150 formed between the plate 143 and theinner burner 105 and the outer burner ports 150 formed between the plate144 and the inner burner 105. As such, the outer burner ports 150 areconsidered to be positioned to the outside of the inner burner ports135.

As shown in FIGS. 2 and 3, the inlet tube 120 is positionable in andremovable from a body 152 of the low NO_(x) burner 100. The body 152includes all of the components of the low NO_(x) burner 100 except forthe inlet tube 120. The inlet tube 120 is received by the inlet 140. Asshown in FIGS. 4-7, the inlet tube 120 includes a cylindrical portion155, a tip 160 at one end of the cylindrical portion 155, and alongitudinal axis 162. The end of the cylindrical portion 155 oppositethe tip 160 is open to receive a fuel/air mixture. The inlet tube 120also includes two locating flanges 165. The flanges 165 define avertical plane that includes the longitudinal axis 162. Alternatively,the inlet tube 120 could include no locating flanges 165, a singlelocating flange 165, or more than two locating flanges 165. The tip 160narrows from a proximal end 172 adjacent to the cylindrical portion 155to a distal end 175. The tip 160 is shorter than the cylindrical portion155 when measured along the longitudinal axis 162. The distal end 175 isclosed so that the fuel/air mixture flowing through the inlet tube 120does not exit the inlet tube 120 in a direction parallel to thelongitudinal axis 162. As shown in FIG. 6, the cylindrical portion 155has a circular cross section. As shown in FIG. 5, the tip 160 has anon-circular cross section that is defined by two curved long sides 180and 185 and two curved short sides 190 and 195. The cross-sectional areaof the tip 160 decreases in size from the proximal end 172 to the distalend 175. Eight openings 200 are formed through the long side 180 andeight openings 200 are formed through the long side 185. The eightopenings 200 through each long side 180 and 185 are positioned in tworows of four. Each row is positioned along a line defined by the centerpoints of the openings 200. Each of these lines is included in a planethat is parallel to the longitudinal axis 162. The size, shape,positioning, and number of the openings 200 can vary. The fuel/airmixture flowing through the inlet tube 120 exits through the openings200. The openings 200 are illustrated as circular holes but can be ofany desired shape, including, but not limited to, non-circular holes andelongated slots.

The inlet tube 120 is inserted in the inlet 140 to position the inlettube 120 such that the longitudinal axis 162 of the inlet tube 120 iscollinear with the longitudinal axis 153 of the inlet 140. Each flange165 is received by a corresponding slot 154 to rotationally position theinlet tube 120 about the longitudinal axis 153. This rotationalpositioning can be accomplished with more or fewer flanges 165 than thetwo illustrated flanges 165. More or fewer locating slots 154 are formedin the inlet 140 as needed. The channel 137 of the inner burner 105includes a stop 141 that engages the distal end 175 of the tip 160 toposition the inlet tube 120 longitudinally within the inlet 140. Theperimeter of the channel 137 is shaped substantially identically to thecross section of the inlet tube 120 through the vertical plane includingthe longitudinal axis 162.

Three alternative embodiments of an inlet tube 220, 320, and 420 of theinlet tube 120 are shown in FIGS. 8-17. FIGS. 8-11 show an inlet tube220 including a cylindrical portion 225, a tip 230 at one end of thecylindrical portion 225, and a longitudinal axis 235. The end of thecylindrical portion 225 opposite the tip 230 is open to receive thefuel/air mixture. The tip 230 narrows from a proximal end 240 adjacentto the cylindrical portion 225 to a distal end 245. The tip 230 islonger than the cylindrical portion 225 when measured along thelongitudinal axis 235. The distal end 245 is closed so that the fuel/airmixture flowing through the inlet tube 220 does not exit the inlet tube220 in a direction parallel to the longitudinal axis 235. As shown inFIG. 10, the cylindrical portion 225 has a circular cross section. Asshown in FIG. 9, the tip 230 has a non-circular cross section that isdefined by two curved long sides 250 and 255 and two curved short sides260 and 265. The cross-sectional area of the tip 230 decreases in sizefrom the proximal end 240 to the distal end 245. Six openings 270 areformed through the long side 250 and six openings 200 are formed throughthe long side 255. The openings 270 through each long side 180 and 185are positioned in a row. Each row is positioned along a line defined bythe center points of the openings 270. Each of these lines is includedin a plane that is angled with respect to the longitudinal axis 235. Thesize, shape, positioning, and number of the openings 270 can vary. Thefuel/air mixture flowing through the inlet tube 220 exits through theopenings 270. The openings 270 are illustrated as circular holes but canbe of any desired shape, including, but not limited to, non-circularholes and elongated slots. For a low NO_(x) burner 100 using the inlettube 220, the size and shape of the channel 137 and stop 141 of theinner burner 105 are modified from what is shown in FIG. 3 to correspondto inlet tube 220. Alternatively, the inlet tube 220 includes locatingflanges 165 in a manner similar to the inlet tube 120.

FIGS. 12-16 show an inlet tube 320 including a cylindrical portion 325,a tip 330 at one end of the cylindrical portion 325, and a longitudinalaxis 335. The end of the cylindrical portion 325 opposite the tip 330 isopen to receive the fuel/air mixture. The tip 230 narrows from aproximal end 340 adjacent to the cylindrical portion 325 to a firststepped portion 350 and narrows again from the first stepped portion 350to a second stepped portion 355 that includes a distal end 345 of thetip 330. The tip 330 is shorter than the cylindrical portion 325 whenmeasured along the longitudinal axis 335. The distal end 345 is closedso that the fuel/air mixture flowing through the inlet tube 320 does notexit the inlet tube 320 in a direction parallel to the longitudinal axis335. As shown in FIG. 15, the cylindrical portion 325 has a circularcross section. As shown in FIG. 14, the first stepped portion 350 has anon-circular cross section that is defined by two flat sides 360 and 365and two curved sides 370 and 375. The flat sides 360 and 365 each definea plane that is parallel to the longitudinal axis 335. An opening 380 isformed through the flat side 360 and an opening 380 is formed throughthe flat side 365. The cross-sectional area of the tip 330 decreasesfrom the proximal end 340 to the end of the first stepped portion 350closest to the cylindrical portion 325. The cross-sectional area of thefirst stepped portion 350 is constant. The cross-sectional area of thetip 330 decreases from the end of the first stepped portion 350 furthestfrom the cylindrical portion 325 to the end of the second steppedportion 355 closest to the cylindrical portion 325. As shown in FIG. 13,the second stepped portion 355 has a non-circular cross section that isdefined by two flat sides 385 and 390 and two curved sides 395 and 400.The flat sides 385 and 390 each define a plane that is parallel to thelongitudinal axis 335. An opening 405 is formed through the flat side385 and an opening 405 is formed through the flat side 390. The size,shape, positioning, and number of the openings 380 and 405 can vary. Thefuel/air mixture flowing through the inlet tube 320 exits through theopenings 380 and 405. The openings 380 and 405 are illustrated ascircular holes but can be of any desired shape, including, but notlimited to, non-circular holes and elongated slots. For a low NO_(x)burner 100 using the inlet tube 320, the size and shape of the channel137 and stop 141 of the inner burner 105 are modified from what is shownin FIG. 3 to correspond to inlet tube 320. Alternatively, the inlet tube320 includes locating flanges 165 in a manner similar to the inlet tube120.

FIG. 17 shows an inlet tube 420 including a cylindrical portion 425, awall 430 at one end of the cylindrical portion 425, and a longitudinalaxis 435. The wall 430 is flat and defines a plane perpendicular to thelongitudinal axis 435. The end of the cylindrical portion 425 oppositethe wall 430 is open to receive the fuel/air mixture. Fourteen openings440 are formed through the wall 430. The openings 440 allow the fuel/airmixture flowing through the inlet tube 420 to exit the inlet tube 420 ina direction parallel to the longitudinal axis 435. The size, shape,positioning, and number of the openings 440 can vary. The openings 440are illustrated as circular holes but can be of any desired shape,including, but not limited to, non-circular holes and elongated slots.For a low NO_(x) burner 100 using the inlet tube 420, the size and shapeof the channel 137 of the inner burner 105 is modified from what isshown in FIG. 3 to correspond to the inlet tube 420. The channel 137cannot include a stop 141 that covers the openings 440 because thefuel/air mixture must be able to exit the inlet tube 420 through theopenings 440. Alternatively, the inlet tube 420 includes locatingflanges 165 in a manner similar to the inlet tube 120.

In use, a fuel-rich fuel/air mixture is supplied to the inlet 140 and afuel-lean fuel/air mixture is supplied to the inlet 125. The fuel can benatural gas, propane, kerosene, methane, or another fuel suitable forcombustion. The fuel-rich mixture is ignited at the outer burner ports150 to form a series of fuel-rich flames. The fuel-rich flames burn at arelatively low temperature compared to stoichiometric flames, therebyreducing the amount of NO_(x) caused by the fuel-rich combustionrelative to stoichiometric combustion. The fuel-lean mixture is ignitedat the inner burner ports 135 to form a series of fuel-lean flames. Thefuel-lean flames burn at a relatively low temperature compared tostoichiometric flames, thereby reducing the amount of NO_(x) caused bythe fuel-lean combustion relative to stoichiometric combustion.Additionally, the fuel-rich flames and the fuel-lean flames interact toform an overall flame that results in a reduced burner noise level ascompared to a burner with stoichiometric flames. Alternatively, afuel-lean fuel/air mixture is supplied to the inlet 140 and a fuel-richfuel/air mixture is supplied to the inlet 125.

Using different inlet tubes 120, 220, 320, and 420 with the low NO_(x)burner 100 allows the low NO_(x) burner 100 to be modified quickly fordifferent applications or combustion characteristics. A “different”inlet tube 120, 220, 320, and 420 can be a different embodiment of theinlet tube 120, 220, 320, and 420 or can be a variation of the sameinlet tube 120, 220, 320, and 420. For example, an inlet tube 120including eight openings 200 through each long side 180 and 185 of thetip 160 is a different inlet tube than an inlet tube 120 including sixopenings 200 through each long side 180 and 185 of the tip 160. Eachinlet tube 120, 220, 320, and 420 causes a restriction in the flow path.Changing from one inlet tube 120, 220, 320, and 420 to a different inlettube 120, 220, 320, and 420 changes the restriction. Changes in therestriction change the rate at which the fuel/air mixture is supplied tothe burner ports 150 and also change the volume of fuel/air mixturesupplied to the burner ports 150. Therefore, a user is able to adjustthe rate and the volume of the fuel-rich fuel/air mixture supplied tothe burner ports 150 relative to the rate and the volume of thefuel-lean fuel/air mixture supplied to the burner ports 135 by changingthe inlet tube 120, 220, 320, and 420.

The low NO_(x) burner 100 allows the user to easily adjust the balanceof the fuel-rich mixture relative to the fuel-lean mixture in order toachieve a desired result by using a different inlet tube 120, 220, 320,and 420. Desired results can include, for example, lower NO_(x) or COemissions, optimizing the burner 100 for use with a specific fuel, andoptimizing the burner 100 for use at a specific elevation. For example,under current California regulations, a burner for a residential type,natural gas-fired water heater is considered to be low NO_(x) whenNO_(x) emissions are less than or equal to forty nanograms per joule ofheat output. The adjustability of the low NO_(x) burner 100 provides foradvantages for design, testing, tooling, and manufacturing. Theseadvantages include savings in development, tooling costs, andmanufacturing costs as compared with other lean-rich dual burnerassemblies.

For the design and prototype testing processes, rather than needing tomanufacture a new burner in order to make adjustments to the relativebalance between the fuel-rich mixture and the fuel-lean mixture, theuser only needs to use a different inlet tube 120, 220, 320, and 420 ormodify an inlet tube 120, 220, 320, and 420 for the low NO_(x) burner100. This makes the low NO_(x) burner 100 much more convenient forprototyping and testing as compared with other lean-rich dual burnerassemblies.

For the tooling and manufacturing processes, the low NO_(x) burner 100provides increased manufacturing flexibility that can reduce the amountof tooling necessary to manufacture a low NO_(x) burner 100. A lowNO_(x) burner 100 can be manufactured for a specific end use byinserting an inlet tube 120, 220, 320, and 420 for that end use into aburner body 152. Rather than needing to manufacture a variety of burnersfor a variety of end uses, the manufacturer is able to manufacture avariety of different inlet tubes 120, 220, 320, and 420 for a variety ofend uses and a common burner body 152.

Alternatively, a removable baffle is used with the low NO_(x) burner 100instead of a removable inlet tube 120, 220, 320, and 420. Differentremovable baffles are configured to create different restrictions in theinlet 140, thereby providing adjustability of the fuel-rich mixturerelative to the fuel-lean mixture similar to that provided by the use ofdifferent inlet tubes 120, 220, 320, and 420.

In a preferred use, the low NO_(x) burner 100 is used as a component ofa tankless gas-fired water heater 500, for example a high input (e.g.199,000 BTU/hr or above) gas-fired tankless water heater. As shown inFIG. 18, the water heater 500 includes multiple low NO_(x) burners 100,a heat exchanger 505 with a water conduit 510, and an exhaust hood 515.The low NO_(x) burners 100 are connected to a source of fuel and asource of air. The source of air could be the atmosphere near the waterheater 500. A cold water supply pipe 520 is connected to an end of thewater conduit 510 and a hot water supply pipe 525 is connected to theother end of the water conduit 510. The low NO_(x) burners 100 arefluidly connected to the heat exchanger 505 and the exhaust hood 515.

In use, fuel and air are supplied to the low NO_(x) burners 100 andcombusted as described above to create products of combustion. Coldwater is supplied to the water conduit 510 via the cold water supplypipe 520. The products of combustion flow through the heat exchanger 505and are placed in a heat exchange relationship with the water flowingthrough the water conduit 510 so that heat is transferred from theproducts of combustion to the water. The heated water is supplied to thehot water supply pipe 525 for use at an end location, for example, awater faucet. The products of combustion flow out of the heat exchanger505 to the exhaust hood 515 and are eventually vented to atmosphere.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. A low NO_(x) burner comprising: a body includinga plurality of first burner ports connected to a first burner inlet anda plurality of second burner ports connected to a second burner inlet;and a removable inlet tube positioned in the second burner inlet toprovide a fuel/air mixture to the second burner ports; wherein the inlettube includes a cylindrical portion, a longitudinal axis, and aplurality of openings, the openings positioned in a plane nonparallel tothe longitudinal axis.
 2. The low NOx burner of claim 1, wherein thesecond burner ports are positioned to the outside of the first burnerports.
 3. The low NOx burner of claim 1, wherein: the inlet tube furtherincludes a tip extending from an end of the cylindrical portion; the tipincludes a closed distal end; and the openings are formed in the tip. 4.The low NOx burner of claim 1, wherein the openings are formed in an endof the cylindrical portion.
 5. A tankless gas-fired water heatercomprising: a burner including a body with an inner burner having afirst burner inlet and an outer burner having a second burner inlet anda removable inlet tube positioned in one of the first burner inlet andthe second burner inlet, the removable inlet tube having an arrangementof openings to provide a desired fuel/air mixture to one of the innerburner and outer burner, the burner having an input of greater than199,000 BTU per hour and operable to generate products of combustionhaving desired characteristics resulting at least in part from theremovable inlet tube utilized; a heat exchanger for receiving theproducts of combustion from the burner; and a water conduit positionedin the heat exchanger in a heat exchange relationship with the productsof combustion; wherein the removable inlet tube includes a cylindricalportion, a longitudinal axis, and a plurality of openings, the openingspositioned in a plane nonparallel to the longitudinal axis.
 6. Thetankless gas-fired water heater of claim 5, wherein the desiredcharacteristics include NO_(x) emissions less than or equal to fortynanograms per joule of heat output.
 7. The tankless gas-fired waterheater of claim 5, wherein the removable inlet tube is positioned in thesecond burner inlet to provide the desired fuel/air mixture to the outerburner.
 8. The tankless gas-fired water heater of claim 5, wherein: theinlet tube further includes a tip extending from an end of thecylindrical portion; the tip includes a closed distal end; and theopenings are formed in the tip.
 9. The tankless gas-fired water heaterof claim 5, wherein the openings are formed in an end of the cylindricalportion.